There are several known techniques for attempting to reduce, eliminate or stimulate hair growth in human skin. A few of these known techniques are scientifically proven and widely accepted as effective. However, their degree of efficacy varies greatly.
There are several processes which may be used for producing preferential damage of the hair. In one process the target may be natural melanin pigment in the hair shaft and surrounding supporting tissues. In another process the target may be an external chromophore or contaminant. Most of these processes tend to damage the hair, either by producing heat or by photo-acoustical shock waves. These known processes have varying degrees of effectiveness, but require multiple treatments and, in their current form, produce only partial permanent hair reduction.
In recent years the use of light sources to reduce or eliminate unwanted hair growth has been developed. One known technique selects a wavelength of laser light that is well-absorbed by the naturally occurring “native” pigments in the hair shaft (and perhaps some pigment in parts of the hair duct or hair follicle cells).
Another known technique uses a short pulsed laser to produce a wavelength that may be absorbed by a “foreign” material or “skin contaminant”. Aspects of this technique are described, for example, in U.S. Pat. No. 5,423,803, U.S. Pat. No. 5,817,089, U.S. Pat. No. 5,425,728, U.S. Pat. No. 5,226,907, and U.S. Pat. No. 5,752,949, all of which are incorporated by reference. This contaminant may be applied directly onto the skin and may be introduced into the empty space surrounding the hair shaft. One contaminant that has been used is carbon graphite in particulate form. The graphite particles have a diameter that is small enough to enable the particles to drop from the surface of the skin into the free empty spaces between the duct and the hair shaft. The energy from a laser may then interact with the contaminant particles. This causes injury to surrounding tissues whose function is to support the growth of the hair shaft. This tends to reduce or eliminate hair growth.
These contaminant particles are not physically incorporated into the hair shaft or into the surrounding hair follicle, hair bulge or hair duct cells. Nor do these contaminant particles chemically, immunologically, biologically or otherwise interact, react or complex with the hair shafts or tissue cells. The contaminant particles simply physically occupy the space surrounding the hair shaft.
Another known hair removal technique is to use a pulsed electromagnetic radiation source to produce a wavelength that may be absorbed by hair, as described, for example, in U.S. Pat. No. 5,683,380, which is incorporated by reference.
There are problems with present light and laser hair removal techniques. Known melanin targeting systems work reasonably well and are reasonably safe only when the color of the hair is very dark and when the skin is very light and not tanned. Virtually all light sources which tend to target melanin are also inherently absorbed by the overlying and surrounding skin. At present, these light sources cannot be safely used at optimal very high power settings for people with darker skin or even people with a dark tan.
Dying the hair allows increased damage to the hair target, helps confine damage to the hair target, and enables the use of power settings that are not so high as to damage surrounding and overlying skin. Treatments which target melanin inherently do not work well on light hair, since there is not enough natural pigment to absorb enough energy to damage hair even if the power is quite high. Using hair dye enables this obstacle to be overcome.
A known hair removal process which uses a 1064 nm laser to produce a wavelength that may be absorbed by a skin contaminant appears to be safe on all skin colors, including darker skin colors. However, this safety is a consequence of there being very little melanin absorption. It is therefore necessary to add graphite particles in oil contaminant lotion before laser treatment. This graphite particle lotion does not enter into the hair shaft itself. Instead, the graphite lotion tends to occupy empty spaces surrounding the hair shaft as it sits in the hair duct. This presents a problem. Either an insufficient or sub-optimal number of graphite particles penetrate into the hair duct, or an insufficient amount of damage is caused by the graphite particles. Consequently, many treatments tend to be required before an acceptable result is achieved.